. A device generally used in a cathode-ray or camera tube to emit a stream of electrons moving at uniform velocity in a straight line. It consists of an emitting cathode and an anode, with an aperture for passage of some of the electrons. 2
. A device used in electron-beam evaporation, comprising a heated cathode to generate the electrons, a high-voltage system to accelerate the electrons, a water-cooled crucible containing the material to be evaporated, and electromagnets to deflect the electrons into the crucible.